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Thanks to Dr. Pooja Navale, Icahn School of Medicine at Mount Sinai, New York, New York (USA), for contributing this case and Dr. Kelly Magliocca, Emory University, Atlanta, Georgia (USA), for writing the discussion.

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Clear cell odontogenic carcinoma is a rare odontogenic malignancy occurring within an intraosseous location of the maxilla or mandible. It exhibits perfect morphologic, immunohistochemical and molecular overlap with CCC, making anatomic site the main distinguishing feature between these two entities.

Mucoepidermoid carcinoma mimics clear cell caricnoma, particularly when occurring in a minor salivary gland location such as the base of tongue or palate with a clear cell component. CCC generally lacks epidermoid cells with abundant eosinophilic cytoplasm and, although occasional mucous cells have been described in CCC, the presence of numerous mucous cells lining cystic spaces or forming discrete clusters would be unusual in CCC. On a molecular level, CRTC1-MAML2 or CRTC3-MAML2 fusion genes are seen in most cases of MEC, but EWSR1-ATF1 gene fusion most commonly characterizes CCC.

Among metastases to the head and neck region, renal clear cell carcinoma (RCC) is not uncommon. Metastatic RCC is most frequently identified in the nasal cavity/paranasal sinus and oral cavity, although involvement of the oropharynx has also been reported (Head Neck Pathol 2009;3:217). Deposits of metastatic RCC exhibit prominent sinusoids, lack hyalinization of the stroma and highlight with vimentin, PAX8 and CD10, in contrast to CCC.

More common in major salivary glands, epithelial-myoepithelial carcinoma (EMCA) can be distinguished by the presence of an abluminal population of myoepithelial cells with clear cytoplasm surrounding the epithelial (ductal) population. The multinodular pattern of growth described in EMCA would be unusual in CCC. The myoepithelial elements of EMCA exhibit reactivity to S100, SMA, calponin, SOX10 and GFAP, markers that would be absent in CCC.

CCC is generally regarded as a low grade malignancy, although nodal metastasis may occur in 25%. Distant metastasis and reports of high grade transformation (with EWSR1 rearrangement) have been reported (Cancer 2009;115:75).

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